The present invention relates to balancing of rotors of large dynamoelectric machines and, more particularly, to in situ balancing of a rotor of an alternator operatively coupled to a shaft of an internal combustion engine and assembled in a locomotive.
Balancing of rotating apparatus, from automobile tires to aircraft gas turbine engines, is a generally known process. Typically, the apparatus is placed on some form of fixture and rotated at preselected speeds. The fixture has built-in electronics for detecting out of balance conditions and indicating to an operator a mass of weight and the location for adding the mass so as to correct the unbalance condition. Some of these balancing machines may provide for gross corrections, such as with tire balancing, while others may provide for very fine balancing, such as is required for gas turbine engines. The first may sense the forces induced in the machine by the rotating apparatus while the latter may use highly expensive, non-contacting vibration sensing equipment, such as dynamic trim balancing analyzers of the type described in U.S. Pat. No. 3,751,987. These latter type machines, while very accurate, are not generally adapted for use in detecting unbalance in large dynamoelectric machines mounted in an operating system. Initial balancing of rotors of large dynamoelectric machines is generally performed in the same manner as with other rotating apparatus, i.e., before installation in an operating system. However, such initial balancing is often not sufficient to meet the requirements for vibration when the rotor is installed in the dynamoelectric machine and further installed in an operating environment. In particular, when the rotor is operatively coupled to a shaft of an internal combustion engine, the additional vibration induced by the engine may be sufficient to excite undesirable vibrations in the dynamoelectric machine and in the equipment in which the machine is installed. Accordingly, it would be advantageous to provide a method and apparatus which can be used in a manufacturing environment to detect and correct unbalance in a large dynamoelectric machine when the machine is installed in an operating locomotive or similar electric traction vehicle.